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GCSE Chemistry · key term
An electronic instrument that uses a probe to measure pH and displays a numerical value.
Used by OCR
Specification C3.3k · Paper 1 (Foundation), Paper 3 (Higher)
Revise: Measuring pHTwo important ways to measure pH are universal indicator and a pH meter. Both respond to the chemical conditions in the solution, but they produce different kinds of evidence.
Paper 1 (Foundation), Paper 2 (Foundation), Paper 3 (Higher), Paper 4 (Higher)
An electronic instrument that measures the pH of a solution and displays a numerical value.
Revise: pH scaleA pH meter uses an electronic probe and displays a numerical pH value. Before use, it is calibrated using reference solutions of known pH. The probe is then rinsed to avoid contaminating the sample, placed in the solution and left until the reading is stable.
When asked to describe measuring pH, name the apparatus and explain how the result is obtained: compare a universal-indicator colour with a pH colour chart, or read the value from a calibrated pH meter.
If comparing methods, state that a pH meter provides a numerical, more precise reading, but it must be calibrated and used correctly.
Universal indicator gives an approximate pH from a colour chart, whereas a calibrated pH meter provides a numerical measurement.
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